The present invention relates to an X-ray apparatus.
Conventional X-ray apparatus have simultaneous heating/exciting system and a preheating system. In the simultaneous heating/exciting system, a current is supplied to the filament of an X-ray tube when the X-ray switch is turned on. A high voltage, i.e., a tube voltage, is simultaneously impressed between the cathode and anode electrodes of the X-ray tube. In the preheating system, when the X-ray switch is turned on, the filament is first heated and a tube voltage applied between the cathode and anode electrodes after a predetermined period of time. With the simultaneous heating/exciting system, there is a delay of approx. 0.1 to 0.3 sec. from the time the X-ray switch is turned on to the time the filament reaches a predetermined temperature thereby causing X-ray radiation. Also, since the X-ray output level increases as the temperature of the filament rises, the X-ray output radiation level will vary until it reaches a preset X-ray output level.
With the preheating system, since the filament is preheated, when a tube voltage is impressed between the anode and the cathode, a predetermined level of radiation will be immediately released, thereby obtaining a sharp rise. However, this preheating system requires a transformer for heating the filament and a transformer for producing a tube voltage, which costs more than the simultaneous heating/exciting system and increases the size and weight of the apparatus. It is required that an X-ray generator of a dental X-ray apparatus in particular be compact and light in weight for the purposes it is used. Therefore, in the dental usage, one tank includes a high voltage transformer and X-ray tube, a winding for filament heating being located on an iron core of the transformer, and simultaneous heating/exciting systems are employed. However, this simultaneous heating/exciting system produces an obtuse X-ray output as described above and energizes the filament at the time of X-ray radiation. Accordingly, the temperature of the filament will vary depending on the condition when heating is started, and the radiation time and the X-ray output level transition will vary every time the apparatus is started. When the X-ray apparatus is, for example, initially operated, the filament is at ambient temperature, and after stopping operation the temperature will correspond to the length of the cooling period. In this manner, the X-ray radiation time and the rising time will vary depending on the X-ray radiation conditions. Therefore, the simultaneous heating-exciting system has a short X-ray radiation period, particularly, when performing a short time X-ray radiation, causing error in the X-ray radiation amount due to this irregularity and causes irregular radiation. In other words, the simultaneous heating/exciting system does not radiate a constant amount even when the radiation period is short.
Further, the above-mentioned error in short X-ray radiation has a great affect on film sensitivity, on restriction of irregular radiation dosage and on increases in X-ray source output. Therefore, it is desired to improve the reproducibility of the amount of radiation of X-rays during short radiation periods. Conventional dental X-ray apparatus, in particular require small size and low cost as well as good reproducibility of X-ray radiation amount.